This invention relates in general to means and apparatus for controlling the air introduction into furnaces and in particular into gas furnaces which typically have a plurality of evenly spaced burners.
The design of heating units, such as gas furnaces, involves considerations of fuel efficiency, and operational economy. One objective is to obtain the maximum amount of heat from a volume of fuel and to efficiently conduct that heat to areas of the residence or building which are below the desired temperature. As the fuel is burned, heat is generated by the combustion process and by heat exchange means. This generated heat of combustion is transferred to clean heating air which then circulates through the building. The combustion gases and unburned particles of fuel exit from the furnace and from the building by means of an exhaust flue. The air for combustion enters by way of an open area in the lower region of the furnace adjacent the burner location. Typically, there are no restrictions on this open area and the incoming air establishes an entering velocity based upon pressure differentials created by the rising hot air from within. The flue typically includes an updraft opening at its lowermost end which enhances the "chimney effect" of the flue and allows a higher upward air velocity. This upward air flow increases the evacuation of exhaust fumes and unburned fuel particules from within the combustion chamber of the furnace.
While this foregoing description represents the typical gas furnace arrangement, a number of subtleties exist which may greatly influence fuel economy and overall operational efficiency. One factor involves the aspect of allowing the flue updraft opening to remain open at all times. When this is done any heat retained within the furnace after the furnace is turned off will exit more rapidly due to the updraft created. As this retained heat exits, the overall furnace temperature drops and when the furnace is restarted, a portion of the initial heat generated will be absorbed by the furnace itself rather than being directed to heating of the building. By providing some means to retain heat within the furnace longer, the heat generated by the fuel which is burned will be utilized more efficiently.
Another factor involves the introduction of the air into the burner area of the furnace. There are typically three or four burner locations which are somewhat evenly spaced apart and as air enters, this air is utilized for combustion in the immediate vicinity of the burners. However, a portion of the entering air which does not pass in close proximity to the burners will not be utilized for combustion and will travel somewhat directly through the combustion chamber and up the flue. This increased means flow rate of air which passes in and out through the furnace and is not utilized in any constructive way has a tendency to draw with it certain heated air. This heated air loss occurs before any effective heat transfer can be achieved and thus lowers the overall furnace efficiency. By controlling the amount of air which is introduced into the furnace such that the amount of air corresponds more optimally to just that amount needed for complete combustion, the flow of air through the furnace is reduced and the heat generated within the furnace is retained longer.
Another factor or consideration which finds a certain applicability to the present invention is that any medium which is being burned is burned more efficiently and more completely if the fuel is mixed more thoroughly with the combustion air. In order to enhance such mixing, a certain degree of air turbulence is desired as the air contacts the gas. With a single open area for air introduction into the burner region of the furnace, such air turbulence is not generated to a sufficient degree and consequently, this desirable mixing does not take place to an optimal degree. By the incorporation of a plurality of apertures or air inlet orifices, the turbulence of the incoming air can be increased and this in turn will create a mixing action of both the air and the gas thereby contributing to a more complete combustion and improved fuel utilization.
The following list of patents represent certain furnace controls and systems which have been conceived for a variety of purposes, yet none of the listed references provide the various means or structure to achieve those improvements which have been mentioned.
______________________________________ Patent No. Patentee ______________________________________ 4,155,699 Hansen 2,937,697 Johnston 4,021,187 Schulte et al. 3,999,710 Kemmerer 3,951,051 Dry ______________________________________
Hansen discloses a gas furnace concept which includes means for automatically closing the air inlet to the combustion chamber as well as the air inlet to the diverter air opening at the flue immediately after cessation of the main burner flame and also for opening both of the air inlets immediately prior to the ignition of the main burners.
Johnston discloses a furnace draft control which includes a parallel connection of two solenoids, one of which acts on an air inlet damper to the combustion chamber and the other of which acts on a similar damper arrangement associated with the flue. This arrangement, which is similar to Hansen, also results in simultaneous opening or closing of the two inlet locations.
Schulte et al. discloses a flue gate device which is operated by a solenoid whose energy comes from an outside source and this energy is controlled by the furnace burner control. The solenoid is deenergized when the furnace burner is energized and the solenoid is energized when the burner is deenergized thus enabling a fail-safe condition which enables the furnace to function completely free of the flue gate device.
Kemmerer discloses an auxiliary heating arrangement for a building which includes a solenoid-controlled damper subassembly.
Dry discloses a damper design which is operable by energizing or deenergizing an electrical circuit to open or close the damper for control of smoke ventilation in case of a fire.
These five references do not disclose permanently closing the updraft opening of the flue, a plurality of air inlet apertures adjacent the burner area of the furnace nor means to selectively open and close these apertures; all of which constitute improvements embodied within the present invention and which contribute to greater fuel efficiency and furnace economy. These advantages as well as others will be apparent from the descriptions which follow.